where X is the energy level corresponding to the principal quantum number n, type is a lower-case letter denoting the shape or subshell of the orbital and it corresponds to the angular quantum number l, and y is the number of electrons in that orbital.
For example, the orbital 1s2 (pronounced "one ess two") has two electrons and is the lowest energy level (n = 1) and has an angular quantum number of l = 0. In X-ray notation, the principal quantum number is given a letter associated with it. For n = 1, 2, 3, 4, 5 ....., the letters associated with those numbers are K, L, M, N, O .... respectively.
Physicists and chemists use a standard notation to describe the electron configurations of atoms and molecules. For atoms, the notation consists of a string of atomic orbital labels (eg, 1s, 2p, 3d, 4f) with the number of electrons assigned to each orbital (or set of orbitals sharing the same label) placed as a superscript. For example, hydrogen has one electron in the s-orbital of the first shell, so its configuration is written 1s1. Lithium has two electrons in the 1s-subshell and one in the (higher-energy) 2s-subshell, so its configuration is written 1s2 2s1 (pronounced "one-s-two, two-s-one"). Phosphorus (atomic number 15), is as follows: 1s2 2s2 2p6 3s2 3p3.
For atoms with many electrons, this notation can become lengthy and so an abbreviated notation is used, noting that the first few subshells are identical to those of one or another of the noble gases. Phosphorus, for instance, differs from neon (1s2 2s2 2p6) only by the presence of a third shell. Thus, the electron configuration of neon is pulled out, and phosphorus is written as follows: [Ne] 3s2 3p3. This convention is useful as it is the electrons in the outermost shell which most determine the chemistry of the element.
The order of writing the orbitals is not completely fixed: some sources group all orbitals with the same value of n together, while other sources (as here) follow the order given by Madelung's rule. Hence the electron configuration of iron can be written as [Ar] 3d6 4s2 (keeping the 3d-electrons with the 3s- and 3p-electrons which are implied by the configuration of argon) or as [Ar] 4s2 3d6 (following the Aufbau principle, see below).
The superscript 1 for a singly-occupied orbital is not compulsory.[4] It is quite common to see the letters of the orbital labels (s, p, d, f) written in an italic or slanting typeface, although the International Union of Pure and Applied Chemistry (IUPAC) recommends a normal typeface (as used here). The choice of letters originates from a now-obsolete system of categorizing spectral lines as "sharp", "principal", "diffuse" and "fine", based on their observed fine structure: their modern usage indicates orbitals with an azimuthal quantum number, l, of 0, 1, 2 or 3 respectively. After "f", the sequence continues alphabetically "g", "h", "i"… (l = 4, 5, 6…), although orbitals of these types are rarely required.
The electron configurations of molecules are written in a similar way, except that molecular orbital labels are used instead of atomic orbital labels
Now that you've read all that nonsense, go off and try to work out your own homework rather than have people on a forum tell you the answer.

la-la-lara

29-05-09, 06:37

Now that you've read all that nonsense, go off and try to work out your own homework rather than have people on a forum tell you the answer.

You did not answer to what I asked.

In this schoolyear's chemistry we were taught that all three quantum numbers identify a hydrogen-like atomic orbital. There is no doubt about it. Not until the opening post was actually a multiple-choice question in the Panhellenic Entrance Examination this year. Many experienced chemists stated that only two of the quantum numbers are necessary to identify a hydrogen-like atomic orbital. That's what all this fuss is about.

As you can see, all I wanted was a third opinion.

spikejones

29-05-09, 06:43

10 years since I'v studied this stuff. Obviously none of it stuck :vlol:

MattTR

29-05-09, 06:52

NEVER took chemistry in my life.. but wishing you some good luck. :vlol: